Toxic Exposures and Cancer Risk: Findings From Two Recent Studies

Two recent studies have come out with some interesting and important findings about exposures to endocrine disrupters and our risks for cancer.

One widely-reported study examined the risks for breast cancer associated with the use of hair dyes, which contain endocrine disrupters.

And another study looked at the way exposures to endocrine disrupters are measured. This study was not as widely publicized, but its findings could potentially be very significant.

What are endocrine disrupters?

The term endocrine disrupters covers a wide range of chemicals both natural and synthetic that are present in our environment. These substances interact with the receptors in our body for estrogen and other hormones in ways that are understood to lead to the development of cancer, including breast cancer.

Examples of known endocrine disrupters include the synthetic estrogen DES, dioxins (by-products of various industrial processes), and the pesticide DDT.

Endocrine disrupters also include substances that studies have shown to be associated with cancer risk. One of these substances is bisphenol A (BPA). BPA and similar substances are widely used in plastic bottles and canned food liners. Many studies have found that this chemical is associated with an increase in breast cancer risk, especially when the exposures occur early in life.

Hair dyes and breast cancer risk

Hair dyes are a product frequently used by women, and increasingly by men as well. Hair dyes contain BPAs, and a number of studies have looked at whether using hair dyes increases cancer risk, but the results have been inconsistent.

To better understand this risk, researchers turned to the Sister Study, a cohort of over 50,000 women enrolled between 2003 and 2009 in a large initiative (that remains ongoing) to learn about the causes of breast cancer. None of the women had a personal history of breast cancer at the time they enrolled, but all had sisters who had had a breast cancer diagnosis.

In the current study, researchers examined the use of hair dyes by women enrolled in the Sister Study and whether using hair dye increased their risk for breast cancer. The study found that women who regularly used permanent hair dye were 9% more likely to develop breast cancer than women who didn’t use hair dye. The increase in risk was greatest for African American women in the group, who had a 60% increased risk for breast cancer  when they used permanent hair dye every 5 to 8 weeks or more often.

There are some important caveats with this study. The first is to understand what these increases in relative risk mean. As an example, if a woman’s risk for breast cancer over the next decade is 3%, an increase of 60% would mean that her risk rises to 4.8%.

The other thing to keep in mind is that this group of women is somewhat different from the general population in that all of the women have sisters who had breast cancer diagnoses, so their risk may be higher to begin with.

Measuring our exposures to toxic substances

BPAs or similar substances are also widely used in food and beverage packaging. The FDA does not currently restrict the use of BPAs in food packaging, primarily because studies conducted by the FDA show that levels of this substance in our bodies are very low. But what if there are flaws in the way these exposures are being measured currently?

In another recent study, researchers evaluated a newer technology for measuring BPA exposures. Using this newer method, they found that exposure levels were as much as 44 times the levels found with the older method.

In an article in The Lancet reporting on the study and its findings, the researchers write that the older methods provide the bulk of the data we have now on human BPA levels, but that these new findings provide compelling evidence that human exposure to BPA is far higher than had been assumed based on those methods. They go on to say:

Because negligible exposure levels have been a cornerstone of regulatory decisions, including the FDA conclusion that BPA poses little health risk, the present data raise urgent concerns risks to human health have been dramatically underestimated.

The researchers also pointed out that the measurement discrepancies found for BPA likely extend to other environmental contaminants as well.

What can we take from these findings?

When asked whether women should stop dyeing their hair, study co-author Dale Sandler, Ph.D. said in a statement  “We are exposed to many things that could potentially contribute to breast cancer, and it is unlikely that any single factor explains a woman’s risk. While it is too early to make a firm recommendation, avoiding these chemicals might be one more thing women can do to reduce their risk of breast cancer.”

However, experts such as those on the President’s Cancer Panel have long said that it’s not just one type of exposure, but the impact of cumulative exposures over a lifetime, as well as the interaction of multiple environmental contaminants, that lead to increased cancer risk.

It would seem that is why accurately measuring exposure levels is critical.

Not surprisingly, technologies for measuring exposures have improved over the decades. Updating those measurement techniques and standards seems just as important, if not more so, than any steps individuals might take to reduce use of any one type of product.

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